Because of the low cost, simple structure, low power consumption and small size thereof, the light emitting diode (LED) is applied in display and illumination technologies. AlGaInP LED devices have already attracted considerable attention in red, yellow, orange, and green LED development.
For general AlGaInP LED fabrication, an AlGaInP LED device is formed on a GaAs substrate directly, while a cathode electrode and an anode electrode are respectively fabricated on different sides of the substrate. This conventional structure has a better current spreading efficiency, but an increased device package area is necessary. Therefore, a flip chip AlGaInP LED device has been gradually developed over the last few years.
The p-type semiconductor layer and the n-type semiconductor layer are exposed on the same side of the LED structure in a flip chip AlGaInP LED fabrication to allow the anode electrode and the cathode electrode to be on the same side of the LED, and the LED structure with electrodes can thus be reversed onto a solder directly by flip chip packaging technology. Thus, conventional wire bonding for the package is not necessary, and a smaller package size and higher device reliability are obtained.
However, the light emitted upward from the flip chip AlGaInP LED is absorbed by the GaAs substrate and cannot pass through the GaAs for complete outward output. Therefore, although the flip chip AlGaInP LED is beneficial for device package, the flip chip AlGaInP LED suffers a lowered LED light output intensity.
Further, the field of LED technology is highly focused on the development of LED devices with higher brightness. Unfortunately, only the light emitted upward from the LED counts as light output; the light emitted downward is partially absorbed by the material below the LED device and is not another source for light output. More particularly, the light emitted downward from the flip chip LED is easily blocked and scattered by electrodes. Thus, the light output of the LED only depends on the diode luminance, and the light output intensity is limited in improvement.